1. Field of the Invention
The present invention relates generally to computer disk drives and more specifically to fabrication of the induction coil for use with magnetic write heads.
2. Description of the Prior Art
A computer disk drive stores and retrieves data by positioning a magnetic read/write head over a rotating magnetic data storage disk. The head, or heads, which are typically arranged in stacks, read from or write data to concentric data tracks defined on surface of the disks which are also typically arranged in stacks. The heads are included in structures called “sliders” onto which the read/write sensors of the magnetic head are fabricated. The slider flies above the surface of the disks on a thin cushion of air, and the surface of the slider which faces the disks is called an Air Bearing Surface (ABS).
FIG. 3 shows a detail view of a magnetic head 14. A coil 18 is included which is configured as a single long strip, which is then curved into the coil shape. There is thus an inner-most turn of the coil, which will be referred to, for convenience, as the coil center 34. There is also an outer-most end 36 to which electrical connection is made to pads (not shown). A center connection called the center tab 38 makes an electrical connection to the coil center 34, thus allowing the coil to be energized to create the magnetic field by which writing operations are accomplished. To make electrical connection with the center tab 38, it has been the common practice to create an overpass lead 40 which reaches over the coil 18 and makes this connection to the center tab 38. Although this has been the general practice in the slider fabrication industry, this configuration has several disadvantages.
During fabrication, it is common to create a coil interconnect 39 (not visible in FIG. 3) which refers to the pedestal or layer plated on the location of the coil center tab for the connection of the coil center tab to the overpass lead 40.
During perpendicular and single layer coil longitudinal write head production, the write pole can be formed by the ion milling process. Damage due to ion milling on the coil interconnect, and the tall re-deposition “fence” surrounding the interconnect edges can result. These tall “fences” present problematic areas for subsequent wet processing As a result, solutions from wet processing seeps through areas around the “fences” and attack the expose coil interconnect, causing interconnect materials to be etched away. Prior solutions cannot eliminate this problem completely. In such a small area, such as the central tab, reducing the interconnect metal will lead to reducing the chance of a good contact between the “over passing” lead and the coil interconnect. When poor contact to either the coils or other features such as the electronic lapping guides (ELG) result, the head is scrapped. The longer the small electrical interconnects for the coil and lapping guides are exposed on the wafer, the greater the chance of damage or poor electrical contact resulting. Also, with the overpass lead design, electrical testing of the coil and ELG is not possible until near the end of the manufacturing line. If a problem arises in the coil or ELG processing, it can take up to a few weeks to detect, during which further production is jeopardized.
One of the present inventors has previously addressed this problem by patenting method and apparatus in U.S. Pat. No. 5,486,968 and U.S. Pat. No. 5,761,013 which include a planarization layer having three sections, two of which connect to MR leads and the third of which connects to the inner coil tab of the inductive coil. The overpass lead is thus replaced by planarization layer which passes under the coils. At the time of these earlier inventions, it was thought to be an important advantage of this planarization layer that it provide a flat surface to build the coils upon. Earlier attempts to make an “underpass” lead left lumps in the surface where the coils were to be deposited, which often impaired the quality of coils. Thus the planarization layer was intended to cover most of the area on which the coil was to be deposited, and thus was more extensive than necessary for the purpose of providing an electrical lead to the coil interconnect. Fabrication of an extensive element such as the planarization layer naturally consumes more time and materials than fabrication of an underpass lead of smaller extent, when the underpass lead is not used for the dual purpose of providing an electrical path and also forming a flat platform for construction of the induction coil.
Thus there is a need for a slider having an underpass lead which is not constrained in shape to act as a planarization layer for induction coil fabrication. There is also a need for a simplified method of fabrication for a slider having such an underpass lead.